# Verifying Calculated Results with Estimation

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• 0:01 Verifying Calculated Results
• 0:47 Using Estimation
• 1:39 Estimation Example
• 3:50 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

As enjoyable as math can be, it is sometimes hard to know if you calculated everything correctly. Wouldn't it be nice if there were an easy way to check your answers? In this lesson, you'll learn how to use estimation to double check your work.

## Verifying Calculated Results

Let's face it, when you do work, it's nice to know that you are right. Nothing is worse than turning in something that you worked hard on and then finding out you did it all wrong. The worst is when it was a silly mistake that caused your errors. You could go back and do the opposite operation - for example, subtracting instead of adding - but that takes time that you may not have in class.

Fortunately, there is an easy way to check your work. It usually doesn't involve the more difficult parts of the math that you had to do to calculate your answer but instead has work so easy that your goofy uncle could probably do it. In this lesson, we're going to learn how to use estimation to check for accuracy in calculated work.

## Using Estimation

Some numbers are easier to work with than others. For example, I bet you'd rather multiply something by 100 than by 98, right? Estimation takes advantage of these easy numbers by allowing us to only work with numbers that are close enough to the original but still far enough away to make math easy. Often, that means rounding a number. Remember that when you round a number, you either add or subtract to get the value close to an easier-to-use number. Think about it like going up and down a hill. Once you reach the top of a hill, you're more likely to roll down forward than you are to roll down backward. Estimating is the same math at play. A key is to remember to keep the math easy. Therefore, try to make it a number that is easy to use. My personal favorites are numbers that end with zero.

## Estimation Example

Let's say that you were calculating the product of 532 and 87. Those are some pretty intimidating numbers, and through your hard work and more than a little sweat, you found out that the product is 46,284. That's a big number! Let's use estimation to check our work. First, let's round 532 and 87 to some nearby numbers. 532 rounds to 500, while 87 rounds to 90. Now for the math. Take the three zeroes off, then multiply 5 by 9. You end up with 45. So, throw those zeros back on there, giving you 45,000. 45,000 is actually pretty close to 46,284, so that means that chances are, we are correct!

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